[Sync] Switch ModelTypeStore* from blocking pool to post_task.h

components/sync/model_impl/model_type_store_backend.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/sync/model_impl/model_type_store_backend.h"
 
 #include <utility>
 
 #include "base/files/file_path.h"
 #include "base/lazy_instance.h"
@@ skipping 58 matching lines @@
   void EraseBackend(const std::string& path);
 
  private:
   mutable base::Lock lock_;
 
   std::unordered_map<std::string, ModelTypeStoreBackend*> backends_;
 
   DISALLOW_COPY_AND_ASSIGN(BackendMap);
 };
 
-base::LazyInstance<BackendMap>::DestructorAtExit backend_map =
-    LAZY_INSTANCE_INITIALIZER;
+base::LazyInstance<BackendMap>::Leaky backend_map = LAZY_INSTANCE_INITIALIZER;
 
 scoped_refptr<ModelTypeStoreBackend> BackendMap::GetBackend(
     const std::string& path) const {
   base::AutoLock scoped_lock(lock_);
   auto it = backends_.find(path);
   return (it == backends_.end()) ? nullptr : it->second;
 }
 
 void BackendMap::SetBackend(const std::string& path,
                             ModelTypeStoreBackend* backend) {
@@ skipping 216 matching lines @@
   UMA_HISTOGRAM_ENUMERATION(kStoreInitResultHistogramName, result,
                             STORE_INIT_RESULT_COUNT);
 }
 
 // static
 bool ModelTypeStoreBackend::BackendExistsForTest(const std::string& path) {
   return backend_map.Get().GetBackend(path) != nullptr;
 }
 
 }  // namespace syncer